Ferritin Level Interpreter

What Ferritin Measures

Ferritin is an intracellular iron-storage protein found in virtually every cell of the body. Its primary role is to capture, store, and release iron in a regulated way, preventing free iron from generating harmful reactive oxygen species. A small amount of ferritin circulates in the bloodstream, and this serum ferritin level closely reflects the size of the body's total iron stores — making it the single most sensitive blood test for detecting iron depletion.

Unlike haemoglobin, which only falls once iron stores are severely exhausted, ferritin begins to decline as soon as iron reserves start to shrink. This means you can be iron-deficient for months before anaemia appears. A low ferritin is almost always a reliable sign of insufficient iron stores. Conversely, an elevated ferritin needs careful interpretation: because ferritin is also an acute-phase reactant — produced in larger quantities by the liver during inflammation, infection, or tissue injury — a high result does not automatically indicate iron overload.

Reference Ranges by Sex and Age

Sources: WHO (2020) Serum ferritin concentrations for the assessment of iron status and iron deficiency in populations; Mei Z et al., Lancet Haematol 2017; typical laboratory reference intervals.

Iron Deficiency Without Anaemia

One of the most commonly missed diagnoses in primary care is iron deficiency without anaemia — also called pre-latent or latent iron deficiency. When ferritin falls between approximately 15 and 30 ng/mL, iron stores are depleted enough to impair cellular function and cause symptoms, even though haemoglobin may still be within the normal range. Symptoms can include persistent fatigue, brain fog, hair shedding, cold hands and feet, poor exercise tolerance, restless legs, and brittle nails.

The WHO defines iron deficiency at ferritin below 15 ng/mL in adults. However, research by Mei Z et al. (Lancet Haematol, 2017) and others has shown that many individuals experience functional iron deficiency at ferritin levels up to 30 ng/mL. A practical functional threshold of 30 ng/mL is widely used by clinicians to guide supplementation decisions, particularly in symptomatic patients. This underdiagnosis is especially common in pre-menopausal women, where low ferritin may be dismissed if haemoglobin appears normal.

Ferritin in Athletes

Endurance athletes are disproportionately affected by low ferritin. Two mechanisms are particularly important: exercise-induced hepcidin secretion — a hormone released after prolonged exercise that blocks intestinal iron absorption for up to 24 hours — and foot-strike haemolysis, where repetitive impact destroys red blood cells and accelerates iron losses. Sweat losses and gastrointestinal bleeding in runners compound the problem. As a result, sports medicine practice commonly targets ferritin above 40–50 ng/mL in endurance athletes, with some practitioners aiming for >50 ng/mL in elite performers. These targets are widely cited in the sports medicine literature but are not established by a formal guideline body such as the WHO or a national haematology society.

When Ferritin Is Elevated

A raised ferritin — particularly above 300 ng/mL in men or 200 ng/mL in women — can have multiple causes that require different clinical responses. Common causes include: acute or chronic inflammation (including infections, autoimmune disease, and cancer — ferritin is an acute-phase reactant and can rise dramatically without reflecting iron overload); non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH); excessive alcohol consumption; hereditary haemochromatosis (HFE gene mutations causing iron accumulation); hyperferritinaemia-cataract syndrome and other rare hyperferritinaemia syndromes; repeated blood transfusions; and recent intravenous iron administration. Markedly elevated ferritin above 1,000 ng/mL is a significant clinical finding that warrants investigation for haemochromatosis, hyperinflammatory states (including macrophage activation syndrome), or haematological malignancy. Because inflammation alone can elevate ferritin substantially, always interpret a high ferritin result alongside CRP (to identify inflammation) and transferrin saturation (to assess iron availability), not in isolation.

Restless Legs Syndrome and Ferritin

Iron plays a critical role in dopamine synthesis in the brain, and low brain iron — reflected by low serum ferritin — is a well-established contributor to Restless Legs Syndrome (RLS). The International Restless Legs Syndrome Study Group (IRLSSG) 2018 consensus recommends considering oral iron supplementation in RLS patients with serum ferritin at or below 75 ng/mL. For intravenous iron, the threshold is ferritin ≤75 ng/mL combined with a transferrin saturation below 20%. This threshold is notably higher than the general WHO iron deficiency cutoff, reflecting the higher iron sensitivity of the dopaminergic system. Patients with RLS and ferritin in the 30–75 ng/mL range who are otherwise considered "normal" by their lab reference range may benefit from iron supplementation — this should be discussed with a neurologist or sleep medicine specialist.